The proposed work is to continue the Survey, to collect enough records of cases of childhood cancers with their controls, and so complete the programme of data collection and processing which was formulated over 10 years ago. This is expected to cover ald children in England, Scotland and Wales who develop malignan diseases within 16 years of birth during the period 1953 - 1975. We wis to further investigate the following problems: 1. The relationship between obstetric radiography and childhood cancers. 2. The relationship between virus infections of the child and leukaemia. 3. The relationship between maternal virus infections during the relative pregnancy and childhood malignancy. 4. Congenital defects associated with cancers. 5. Sib concordant and twin concordant cancers. 6. The latent period of cancer growth. 7. Special studies of specific tumours.